Investigation of the interaction between separate calcium feeding and phytase supplementation on growth performance, calcium intake, nutrient digestibility and energy utilisation in broiler starters

The interaction between separate calcium (Ca) feeding and phytase supplementation on performance, coefficient of apparent ileal digestibility (CAID) of nitrogen (N), starch, fat and phosphorus (P), total tract retention (TTR) of Ca and P, and apparent metabolisable energy (AME) in broiler starters was investigated. The effect of phytase on the CAID and TTR of P in birds with access to a separate Ca source was of particular interest. Five dietary Ca concentrations (1.3, 4.3, 7.3, 10.3 and 13.3 g/kg) and two inclusion levels (0 or 1000 phytase units [FYT/kg] of feed) of a 6-phytase were evaluated in a 5 × 2 factorial arrangement of treatments. All diets, based on wheat and soybean meal, were formulated to be equivalent in respect of total and non-phytate P contents (5.7 and 3.0 g/kg, respectively). A total of 480, one-day-old male broilers were allocated to 48 cages (8 birds/cage), and cages were randomly assigned to 10 dietary treatments. Birds were also provided with a source of Ca in a separate feed trough. Increasing dietary Ca concentration decreased (P < 0.05) weight gain and feed intake in diets without phytase with a marked reduction in the diet with 13.3 g Ca/kg, whereas in the phytase-supplemented diets, the reduction in both weight gain and feed intake was gradual up to 13.3 g Ca/kg, resulting in a dietary Ca concentration × phytase interaction. Addition of phytase lowered (P < 0.01) feed per unit gain at all dietary Ca concentrations. During d 8-14, d 15-21, and over the 21 d trial period, consumption of the separate Ca source was reduced (P < 0.001) by increasing dietary Ca concentration, irrespective of phytase addition. Over the 21 d trial period, increasing dietary Ca above 4.3 g/kg decreased (P < 0.05) the total Ca intake (Ca from separate source plus Ca from feed) in diets without phytase, but the total Ca intake in phytase-supplemented diets were similar (P > 0.05). Birds fed 1.3 g Ca/kg diet showed the lowest (P < 0.05) N digestibility, but similar (P > 0.05) to the diets with 4.3 g Ca/kg. No significant (P > 0.05) effect of dietary Ca concentration on the CAID of starch, fat and GE was found. Whilst, increasing dietary Ca concentration reduced (P < 0.05) P digestibility gradually in diets without and with phytase, the reduction in CAID of P was remarkable in the phytase-supplemented diet with 13.3 g Ca/kg. Phytase addition enhanced CAID of N (P < 0.05), fat and GE (P < 0.01), AME and toe ash (P < 0.05). Increasing dietary Ca to 10.3 and 13.3 reduced TTR of P in diets without phytase, whilst all the phytase supplemented diets showed similar (P > 0.05) retention. There was no effect (P > 0.05) of dietary Ca on AME and toe ash. The previously reported Ca-specific appetite in modern broilers and the 'phosphoric' and 'extra-phosphoric' effects of phytase were confirmed in this study. Importantly, the current work highlighted the additive outcome of separate Ca feeding and phytase addition.